The Stepcase Lifehack blog pulls out a trusted tome, Deirdre McCloskey's Economical Writing, and extracts some wisdom from an accomplished economics professor on writing tight sentences that are thrifty with words (unlike, say, this sentence). Here's one bit especially relevant for online writers:

Always ask "So what?" ... Your reader's time is very valuable, and he or she could be doing a lot of different things. They have decided, for whatever reason, to take a look at something you have written ... Hit them between the eyes with why what you have done is important. Convince them immediately that they should keep reading your work instead of picking up something someone else has written or playing with the kids.

What writing or reference books do our more writerly readers go to for inspiration? Share your bookshelf in the comments.